Chemical reactions

Reaction of cadmium with acetic acid

Cd reacts slowly with gaseous acetic acid [5].

Reaction of cadmium with air

Under normal pressure and temperature, Cd does not react with the air. Polished Cd is matted after a while, forming CdO [5].

At 300 °C Cd forms a thin brown gas-permeable coating. The yield increases parabolic with temperature [5].

Cadmium metal burns in air to form cadmium(II)oxide. The burning temperature is above the sublimations temperature of CdO, 1385 °C [5].

2 Cd(s) + O2(g) 2 CdO(s)

Reaction of cadmium with ammonia

Cd does not react with NH3 in its gaseous form until 255 °C. Above 255 °C is unknown. In aqueous solution NH3 dissolves Cd. Cd2+ forms complexes with NH3(aq). The average number of NH3 per Cd is four but varies depending on [Cd2+] and [NH3] [5].

Cd(s) + NH3(g)
Cd(s) + 4 NH3(aq) Cd2+(aq) + ??
Cd2+(aq) + 4 NH3(aq) [Cd(NH3)4]2+(aq)

Reaction of cadmium with arsenic

Gaseous arsenic reacts with solid Cd forming Cd3As2 at around 700 °C [5].

3 Cd(s) + 2 As(g) Cd3As2(s)

Reaction of cadmium with halogens

Cd(s) + F2(g) CdF2(s) [white]

Cd reacts directly with Cl2 in aqueous solution [5].

Cd(s) + Cl2(aq) Cd2+(aq) + 2 Cl(aq)

Cd reacts directly with Br2 in aqueous solution and Br2(g) at 450 °C [5].

Cd(s) + Br2(aq) Cd2+(aq) + 2 Br(aq)
Cd(s) + Br2(g) CdBr2(s) [pale yellow]

Solid Cd does not react with I2(g), but will react with I2(aq). In gas phase Cd and I2 will react forming CdI2. At high temperature and pressure (e.g. a steel bomb) equivalent Cd and I2 will react forming CdI [5].

Cd(s) + I2(aq) Cd2+(aq) + 2 I(aq)
Cd(g) + I2(g) CdI2(g)
2 Cd(g) + I2(g) 2CdI(g)

Reaction of cadmium with hydroxide

Metallic cadmium does not dissolve in aqueous alkalis such as potassium hydroxide, KOH. Cd2+ is precipitated by excess amounts of OH at pH > 7.5 [5]

Cd(s) + OH(aq)
Cd2+(aq) + 2 OH(aq) Cd(OH)2(s)

Reaction of cadmium with hydrobromic acid

Cd reacts with hydrobromic acid forming CdBr2 [5].

Cd(s) + 2 HBr(aq) CdBr2(s) + H2(g)

Reaction of cadmium with hydrochloric acid

Cd reacts with hydrochloric acid forming CdCl2 [5].

Cd(s) + 2 HCl(aq) CdCl2(s) + H2(g)

Reaction of cadmium with hydrofluoric acid

Cd reacts with hydrofluoric acid forming CdF2 [5].

Cd(s) + 2 HF(aq) CdF2(s) + H2(g)

Reaction of cadmium with hydrogen

Cd usually does not react with H2(g). At 450°C H2 is adsorbed in the metal. When the metal has reached max. adsorption the temperature will increase and Cd reacts with H2 [5].

Cd(s) + H2(g) CdH(s) + H·

Reaction of cadmium with hypochlorite

Cd reacts with hypochlorite forming Cd(ClO2)2 and after a while also Cd(ClO3)2 [5].

Cd(s) + 2 HClO2(aq) Cd(ClO2)2(s) + H2(g) Cd(ClO3)2(s)

Reaction of cadmium with nitric acid

Cd does not react with the fumes from concentrated nitric acid [5].

Cd(s) + HNO3(g)

Dilute hot nitric acid will dissolve Cd, forming nitrogen monooxide

3 Cd(s) + 2 NO3-(aq) + 8 H+(aq) Cd2+(aq) + 2 NO(g) + H2O(l)

Reaction of cadmium with phosphorus

Cd reacts with P at elevated temperatures in an exoterm process forming Cd3P2 and CdP2 [5].

4 Cd(s) + P4(s) Cd3P2(s) + CdP2(s)

Reaction of cadmium with ortho- and pyrophosphoric acid

Cd2+ is precipitated by ortho- and pyrophosphoric acid in an acetic acid/acetate-buffer [5].

3 Cd2+(aq) + 2 PO43−(aq) Cd3(PO4)2(s)
3 Cd2+(aq) + P2O74−(aq) + H2O(l) Cd3(PO4)2(s) + 2 H+(aq)

Reaction of cadmium with selenium and selenium compounds

Cd reacts with Se when heated rigorously [5].

Cd(s) + Se(s) CdSe(s)

Cd reacts with H2Se forming CdSe [5].

Cd(s) + H2Se(s) CdSe(s) + H2(g)

Cd reacts with Se2Cl2 forming CdSe. The reaction is slow and requires heat [5].

Cd(s) + Se2Cl2(s) CdSe(s)

Reaction of cadmium with sulfides

In dry air Cd reacts very slowly with H2S forming CdS. The reaction increases with increasing moisture in the air [5].

Cd(s) + H2S(g) CdS(s) [yellow]

In strong acids like HCl and H2SO4, Cd2+ is precipitated by H2S as CdS. It should be noted that the precipitate is not pure but a mixture of CdS-CdCl2 or CdS-CdSO4. The H+ to Cd2+ ratio has a maximum above which the purity decreases with increasing [H+]. Besides HCl and H2SO4, precipitations has also been done successfully with KCN and NH4Cl [5].

Cd2+(aq) + H2S(aq) CdS(s) [yellow]

In ammonia and cyanide under alkaline conditions, Cd2+ is easily precipitated by S2−:

[Cd(NH3)4]2+(aq) + S2−(aq) CdS(s) [yellow] + 4 NH3(aq)
[Cd(CN)4]2−(aq) + S2−(aq) CdS(s) [yellow] + 4 CN(aq)

Reaction of cadmium with sulfur

In gaseous form, Cd and S8 reacts forming CdS. At 130-180 °C solid Cd and S8 reacts explosively, also forming CdS [5].

Cd(g) + S8(g) CdS(g)
Cd(s) + S8(s) CdS(s) [yellow]

Reaction of cadmium with sulfuric acid

Cadmium metal dissolves slowly in dilute sulphuric acid to form Cd(II) ion and hydrogen, H2. In aqueous solution, Cd(II) is present as the complex ion [Cd(H2O)6]2+.

Cd(s) + H2SO4(aq) Cd2+(aq) + SO42−(aq) + H2(g)

Reaction of cadmium with tellurium

Cd reacts rigorously with Te forming CdTe [5].

Cd(s) + Te(s)
~ 700 °C

Reaction of cadmium with water

Cadmium reacts with H2O(g) forming H2(g) at temperatures above 400 °C [5].

Cd(s) + H2O(g) CdO(s) [Reddish-brown]

Cd only reacts very slowly with destilled water (24-48 h for reaction) [5].

Quantitative analysis

Method 3500-Cd C Inductively Coupled Plasma Method [1]. A portion of the sample is digested in a combination of acids. The digest is aspirated into an 8,000 K argon plasma where resulting light emission is quantified for 30 elements simultaneously.

Method limit of detection in water = 0.001 mg/L
Method limit of detection in soil = 0.10 mg/kg